As information processing apparatus are developed, semiconductor devices possessing high integration and rapid response speed may be desired. However, when the semiconductor devices are highly integrated, the semiconductor devices may have unsuitable characteristics. For example, contact resistances at source/drain regions may increase as the size of the source/drain regions and length of gate electrodes decrease. When a semiconductor device has an increased contact resistance, the semiconductor device may not operate at a high response speed and power consumption of the semiconductor device may increase. To address this concern, a method of forming a metal silicide layer on a gate electrode and source/drain regions of a semiconductor device has been suggested. The metal silicide layer comprises a compound of metal and silicon. For example, the metal silicide layer can include tungsten silicide, titanium silicide, cobalt silicide or the like.
In a conventional method of forming a metal silicide layer, after a titanium layer is formed on a substrate or a silicon containing layer by a sputtering process or a chemical vapor deposition (CVD) process, the titanium layer can be thermally treated to be reacted with silicon contained in the substrate or the silicon containing layer, thereby forming a titanium silicide layer on the substrate or the silicon containing layer. However, the titanium silicide layer may exhibit an increased resistance if the titanium silicide layer is damaged during the thermal treatment process. In contrast, a cobalt silicide layer may be widely employed for a semiconductor device because the cobalt silicide layer may exhibit greater chemical stability and greater stable resistance stability relative to titanium silicide. Additionally, the conventional cobalt silicide layer can be formed by a physical vapor deposition (PVD) process.
In a conventional method of forming a cobalt silicide layer, a cobalt layer can be formed on a silicon substrate or a silicon-containing pattern by a PVD process. The silicon substrate or the silicon-containing pattern having the cobalt layer can be thermally treated to yield reacted cobalt with silicon so that the cobalt silicide layer can be formed on the silicon substrate or the silicon-containing pattern. However, the cobalt silicide layer formed by the PVD process may exhibit poor step coverage. In addition, the cobalt silicide layer formed by the PVD process may not have a uniform thickness when the cobalt silicide layer is formed on predefined patterns or in contact holes.
FIG. 1 presents a cross-sectional view illustrating a conventional method of forming a cobalt layer on a substrate by a PVD process.
Referring to FIG. 1, gate patterns 12 are formed on a semiconductor substrate 10. The gate patterns 12 are separated from each other by a predefined spacing distance. Spacers 14 are formed on sidewalls of the gate patterns 12.
A cobalt layer 16 can be formed on an entire surface of the substrate 10 including the gate patterns 12 and the spacers 14. A portion of the cobalt layer 16 between the gate patterns 12 has a relatively thin thickness compared to that of other portions of the cobalt layer 16 on the substrate 10 and on the gate patterns 12.
When the cobalt layer 16 does not have a uniform thickness on the entire surface of the substrate 10, a cobalt silicide layer formed from the cobalt layer 16 may also have an irregular thickness on the substrate 10. As a result, a semiconductor device including the cobalt silicide layer may have poor electrical characteristics.
U.S. Pat. No. 6,346,477 issued to Kaloyeros presents a method of forming a cobalt layer on a silicon layer by a CVD process using [Co(CO)3NO] as a precursor. In this method, the silicon layer is oxidized by a reaction between silicon and by-products, including oxygen, that are generated from the precursor and generated in the CVD process. In particular, an interface oxide layer is formed between the silicon layer and the cobalt layer to inhibit a reaction between silicon and cobalt and prevent the formation of a cobalt silicide layer on the silicon layer, even after a subsequent thermal process is carried out with respect to the cobalt layer. Additionally, H. S. Rhee et al. presents a method of forming a cobalt layer on a silicon layer by a metal organic chemical vapor deposition (MOCVD) process in “Applied Physics Letters Vol. 74, No. 7, 1999.” In this method, examples of cobalt precursors include Co2(CO)8, Co(C5H5)2, Co(C5H5)(CO)2 and CoCF3(CO)4. However, since the cobalt precursors include carbon and oxygen, impurities including carbon and oxygen may be included in a cobalt layer formed on the silicon layer. When the cobalt layer includes these impurities, the cobalt layer may be unsuitable for semiconductor devices because the cobalt layer may possess high specific resistance.